Oil sand comprises bitumen (a heavy oil), water and solids. The bitumen present in the oil sand can be extracted in situ or mined first and then subjected to a water extraction process. It is important to be able to measure the content of bitumen, water and/or solids in oil sand samples, as well being able to quickly determine the bitumen, water and/or solids content of various process streams formed during bitumen extraction.
The Dean-Stark extraction method is currently the gold standard for determining bitumen, water and/or solids content of a sample. A weighed sample is separated into bitumen, water, and solids by refluxing toluene in a Soxhlet extraction apparatus. Condensed toluene and co-distilled water are continuously separated in a trap designed to recycle the solvent through the extraction thimble, dissolving the bitumen present in the sample, while the water is retained in the trap. Full extraction of bitumen from the solids can often take hours to complete. Once the three components have been physically separated, they can be determined by various means.
Given the long analysis time of Dean-Stark extraction, faster methods are often used to monitor a continuous extraction train used for extracting bitumen from oil sand. These fast methods typically sacrifice some accuracy and/or repeatability in order to achieve a shorter analysis time. They often rely on an extraction step, filtration step, and/or drying step to separate various components prior to measurement, which adds to the total analysis time. Extraction process conditions can quickly change within minutes, making ever shorter analysis times desirable.
It is therefore desirable to develop a faster method for measuring the content of bitumen, water and solids with relatively good accuracy (compared to Dean-Stark extraction), good precision, and within as short an analysis time as possible. U.S. Pat. No. 6,630,357 discloses a method of determining the composition of a sample including heavy oil or bitumen and water using low-field NMR. However, the NMR spectrum of the sample must be taken twice, first at a relatively low temperature and then at a relatively high temperature so that a differential spectrum is created. Heating the sample to two different temperatures increases the total analysis time. Further, because only a single type of relaxation time data is measured (i.e., T2), there is less complete use of available NMR relaxation information and the process is less efficient when measuring smaller quantities of bitumen in a sample that may only contain 1-2 wt. % bitumen [see Kantzas, A., “Advances in Magnetic Resonance Relaxometry for Heavy Oil and Bitumen Characterization”, Journal of Canadian Petroleum Technology, 48 (3) 2009, 15-23]. All available NMR contrast (i.e., differences in T1 and T2) is needed to separate signals from bitumen and water molecules under these difficult circumstances. U.S. Pat. No. 7,397,241 discloses a method of determining the content of at least one component of a sample, but the experimental conditions are optimized for measuring fat and water in biological samples, not the widely varying compositions of bitumen and water in the unique matrix of oil sand core and process stream samples.